Shellfish such as oysters and mussels are a highly regarded seafood, both in New Zealand and overseas. The shellfish industry is worth many millions of dollars to the New Zealand economy, and considerable resources and effort goes into the cultivation of shellfish. Oysters in particular, are a particularly valuable crop.
It can be uneconomic to collect shellfish from their natural environment. This is due to the accessibility of their breeding and living environments, as well as varying abundance site to site. Labour costs and time can also be a factor in not being able to harvest from their natural environment.
Overfishing of shellfish in their natural environment is also a concern. Consumers are becoming more aware of the impact of unsustainable harvesting of seafood, and choosing to purchase food which has been harvested in a sustainable manner.
For this reason, a number of marine and freshwater farms are devoted to the cultivation of shellfish, using a number of different methods.
One such method is disclosed in New Zealand Patent No. 511126, which describes a platform which is installed over the seabed. The platform retains shellfish blocks which provides surfaces on which the shellfish grow. The platform, while allowing cultivation of a large number of shell fish, presents a number of issues in its use.
The platform must be placed upon the seabed, and the shellfish blocks transported and installed into the platform. This can require a number of divers with SCUBA gear if the platform is established in relatively deep water. The labour required to facilitate establishment of the platform can be intensive. When harvesting the mature shellfish, the blocks must be removed, and each shellfish individually harvested from the block. Again, this is a labour intensive process.
Also, being relatively fixed in place, the shellfish can, at times, be exposed to sediments and detritus being carried on the prevailing current. This can foul shellfish, and places stress on the shellfish when feeding.
Over time, the platform and its shellfish blocks steadily collects sediment which harbours parasites such as mud worms or flatworms. These can cause disease and parasite infestation of shellfish colonies, ultimately affecting the quality of the shellfish flesh.
Another source of stress for shellfish is overcrowding. The platform method of cultivating shellfish does not allow the shellfish farmer control of the distribution of the shellfish within the platform. Instead there can be uneven distribution of shellfish within the platform, so portions of the platform are densely populated by shellfish.
Shellfish in close proximity to each other, as with most organisms, will compete for natural resources in their environment, particularly food. As shellfish are relatively sedentary once established, they are not necessarily able to remove themselves to a better environment. Therefore it can be appreciated that platform cultivation of shellfish can be a stressful method for raising shellfish, with a detrimental effect on the flesh of the shellfish.
Variations of the platform method of cultivating oysters have been implemented, for example using fixed inter-tidal trays and racks or mesh bags. However, these all have the same problems as the system disclosed in New Zealand Patent No. 511126.
To resolve this, growers have developed growth systems which encourage the cultivation of individual shellfish. A typical example is U.S. Pat. No. 5,579,724, which discloses a holder for an oyster. However, these systems are not ideal.
The oyster holder disclosed by U.S. Pat. No. 5,579,724 is a relatively complex shape and configuration to manufacture. This adds significantly to the costs of manufacture of the holder.
The holder is also designed in such a way that the juvenile oyster spat must be precisely placed for optimum growth of the oyster. This can be time consuming process when commencing the cultivation process.
The configuration of the holder disclosed in U.S. Pat. No. 5,579,724 is such that a build up of sediment, and thus the problems associated with such a build up of sediment as previously discussed above, can occur in the early stages of the oyster's growth.
The holder as disclosed in U.S. Pat. No. 5,579,724 is not specifically manufactured with a mounting means to secure the holder to a growth surface. Instead, a portion of the holder is meant to be bonded to a growing surface in the environment in which the oyster is to be cultivated. Again, this is a time consuming process when commencing the cultivation process.
One method of shellfish cultivation used to address the problems of seabed cultivation of shellfish as exemplified in New Zealand patent No. 511126 is to suspend the cultivated shellfish in the water column via a weighted rope or similar filamentary growth medium. Usually, the rope is anchored or otherwise weighted to the seabed, and the upper portion of the rope is attached to a buoy. This method of aquaculture requires less labour to install and remove the shellfish growth medium. It also reduces the exposure of shellfish to sedimentation and parasites.
A number of apparatus has been developed to utilise this method of cultivating shellfish, such as United Kingdom Patent Application No. 2421884, which is typical of apparatus used in this method of cultivating shellfish. This patent application discloses C-shaped pegs with the ends of the C-peg being forced through a rope. The peg provides surface area on which mussels can anchor themselves using their byssus, which is a sticky threadlike secretion from mussels.
However, although placed in the water column, shellfish being cultivated in this manner can still be exposed to drifting sediment and detritus.
The optimum orientation of shellfish when feeding, is such that when feeding, the open portion of the shellfish is facing downstream of the prevailing current. This reduces particles entering the feeding organs of the shellfish, and also permits easier egress of any oversized particles which enters the feeding organs of the shellfish.
The apparatus disclosed in GB 2421884 does not permit the shellfish to re-orientate itself once it has been established on the peg. Furthermore, there is no control over the distribution of shellfish cultivated on this or similar shellfish aquaculture apparatus. Thus, there is the potential for overcrowding and competitive stress with a resulting detrimental effect on the size and flesh of the shellfish raised in this manner.
Another further disadvantage of this shellfish cultivation apparatus, is that when harvesting the mature shellfish, considerable time and labour is required to remove the collected shellfish from the growth surfaces of the peg.
Another example of apparatus for cultivating shellfish in the water column is United Kingdom Patent Application 2061081. This patent application discloses a mounting device for a shellfish to be used with plastic tape suspended in the water column.
As with U.S. Pat. No. 5,579,724, the mounting device disclosed in this UK application is particularly problematic as it is a relatively complex shape and configuration to manufacture.
When securing the shellfish to the mount, there is little constraint on the adhesive, and therefore there can be spillage of the adhesive onto regions of the shell of the shellfish where the adhesive is not desired. This is a particular concern where adhesive has spilled onto the region of the shellfish where the shell halves meet.
Once the shellfish is secured to the mount, the mount in turn fixed to the tape. This requires time consuming manipulation of the mount in order to secure the mount to the tape adequately.
The tape itself must also be precisely constructed with apertures complementary to the mount, adding to the expense of manufacture.
Although the plastic tape used in this method of cultivating shellfish is durable and long lasting, it is this particular characteristic which also presents particular environmental problems when harvesting the mature shellfish. As the shellfish is collected, the tape and its mount, designed specifically for one time use, is simply discarded, creating considerable waste.
Portions of both the tape and mount may be damaged or broken away during harvesting, and these portions become flotsam in the marine environment.
Another facet of shellfish cultivation which is not adequately addressed by the prior art is the tagging or identification of the shellfish. It is desirable to have the ability to mark cultivated shellfish in some way to allow the shellfish to be traced in the event of a product recall.
Shellfish is a food which can easily become contaminated. It is a matter of public safety to be able to identify and recall shellfish which is at risk of contaminating the general public if consumed.
Marking of shellfish product can also be used as a promotional aid, to inform the consumer of the origin of the shellfish. This would be particularly important for regions which have a reputation for high quality seafood such as oysters coming from Bluff, New Zealand.
Current systems for labelling of shellfish are limited. For example, New Zealand Patent No. 531711 provides a tag which becomes incorporated into the shell portion of the shellfish as it matures.
This particular method of marking is limited to electronic identification, as the surface area of the tag does not permit the application of lettering or similar markings. In any event, the tag becomes partially integrated with the shell, and may become difficult to read.
Any lettering or other markings on the tag becomes fouled over time, thus becoming illegible. Considerable cleanup is required in order to make the markings readable.
This is particularly the case with the oyster holder disclosed in U.S. Pat. No. 5,579,724, discussed earlier in this specification. The holder is provided with a small, flat surface on one side of the holder on which markings can be applied. However, dirt and organisms such as algae can foul this area, making the markings illegible. Careful cleaning is required to make the markings readable, but without destroying the markings during the cleaning process.
If the tag is a RFID tag, electronic equipment is required to read the information stored on the tag.
Other methods of labelling, such as adhesive labels, require that the shellfish be sufficiently dry for the adhesive to become securely fastened to the shellfish. This would be extremely labour and time intensive to achieve, and would add substantially to the harvesting cost of the shellfish, a cost which would then have to passed onto the consumer.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.